In the Swedish patent specification No. 199,167, published Oct. 26, 1965, a steel alloy with high high-temperature strength is disclosed. This steel contains in percent by weight:
______________________________________ 0.20-0.50 C 0.2-0.5 Si 2-3 Cr 2-3 Mo, which wholly or partly may be replaced by tungsten in the ratio 1:2 0.3-0.6 V 2-3 Co ______________________________________
This known alloy, however, has an unsatisfactory resistance to tempering. The ever higher demands which are imposed by the present day technology insofar as better strength properties are concerned, also have given rise to the developement of a number of modifications and alternatives to the above alloy. By way of example, reference may be made to the steel alloys disclosed in the Swedish patent specifications Nos. 364,997, 364,998, and 364,999 (published Mar. 11, 1974), which besides iron are characterized by the following compositions (weight percent):
______________________________________ SE 364 997 SE 364 998 SE 364 999 ______________________________________ C 0.030-0.45 0.35-0.45 0.3-0.4 Si 0.2-1.0 0.2-0.5 0.2-0.5 Mn 0.2-1.0 0.8-1.5 0.1-0.5 Cr 2.0-3.5 1.0-1.8 1.0-2.0 Mo 1.0-2.0 2.5-3.5 1.5-3.0 W 2.0-3.0 V 1.0-1.5 1.0-1.3 0.4-0.8 Nb 0.1-0.5 -- -- B 0.002-0.01 0.003-0.01 0.001-0.1 Co 1.5-3.0 1.5-2.5 1.5-2.5 ______________________________________
As compared to the first mentioned alloy the above alloys generally exhibit improved strength properties, however, without offering a combination of features optimal for hot work steels. Moreover (and this also pertains to the first mentioned Swedish patent specification No. 199,167) the properties are obtained at the price of a comparatively high content of expensive alloying elements, among which in the first place the high cobalt contents have a dominating influence on the total costs of alloying elements.